<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    .outer{
      width: 1000px;
      height: 900px;
      background-color: #888;
      margin: 0 auto;
      display: flex;
    }
    .inner{
      width: 200px;
      height: 200px;
      background-color: skyblue;
      border: 1px solid black;
      box-sizing: border-box;
    }
    .inner2{
      flex-basis: 1000px;
    }
  </style>
</head>
<body>
<div class="outer">
  <div class="inner">1</div>
  <div class="inner inner2">2</div>
  <div class="inner">3</div>
</div>
</body>
</html>